Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Silicon containing or process of making
Reexamination Certificate
1999-06-25
2001-11-13
Bell, Mark L. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Silicon containing or process of making
C502S233000, C502S245000, C502S262000, C502S243000, C502S250000, C502S439000, C502S527140, C502S527160, C428S034400, C428S034600, C106S482000, C501S133000
Reexamination Certificate
active
06316383
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is based on German Application DE 198 28 491.8, filed Jun. 26, 1998, which disclosure is incorporated herein by reference.
FIELD OF THE INVENTION
This invention relates to moldings based on silica, to a process for their production, and their use as a catalyst for the acetoxylation of olefines.
BACKGROUND OF THE INVENTION
Silicas, particularly pyrogenic silicas, are characterized by their extremely finely divided state and their correspondingly high specific surface, by their very high purity, by their spherical particles and by the absence of pores. Due to these properties, there is an increasing interest in pyrogenic silicas as supports for catalysts (D. Koth, H. Ferch, Chem. Ing. Techn. 52, 628 (1980)).
It is known from DE-B 21 00 778 that granular materials based on pyrogenic silicas can be used as catalyst supports for the production of vinyl acetate monomer.
It is known from DE-A 38 03 900 that cylindrical particles which have arched end faces and which are based on pyrogenic silicas can be used as catalyst supports for the production of vinyl acetate monomer.
A process for the production of pressed parts is known from DE-A 39 12 504 in which aluminum stearate, magnesium stearate and/or graphite are used as a lubricant, and in which urea as well as methyl cellulose are used as pore forming agents.
These known pressed parts which are produced with magnesium stearate are commercially available as Aerosil Tablets No. 350, as supplied by Degussa. They contain about 0.4% by weight Mg.
Catalyst supports for catalysts for the synthesis of vinyl acetate monomer are known from EP 0 004 079 which consist of extruded sections with a star-shaped cross-section or which consist of ribbed lengths.
Catalysts for the synthesis of vinyl acetate monomer, which comprise at least one passageway channel with an inside diameter of at least 1 mm, are known from EP-B 464 633.
DE-A 195 38 799 describes a catalyst support in the shape of a honeycomb which predominantly consists of SiO
2
. According to Example 1 of said patent, this support has a diameter of 25 mm, a stay width of 1 mm, a stay spacing of 2 mm, and a length of 150 mm. After being coated with catalytically active elements, the resulting catalyst can be used for the production of unsaturated esters from olefins, acids and oxygen in the gas phase, for the purification of off-gas contaminated by organic substances, and for the alkylation of aromatic compounds.
WO 97/36679 also describes a catalyst support in the shape of a honeycomb, which is coated with SiO
2
and which, after impregnation with palladium and gold and after activation with potassium acetate, can be used for the production of unsaturated esters.
Honeycomb-shaped catalysts are characterized by a very low pressure drop. However, the use of honeycomb-shaped catalysts in industrial reactors, particularly in tube bundle reactors, results in problems which are not inconsiderable, particularly with regard to packing tube reactors. With tube reactors, it is sometimes necessary to pack several thousand tubes of an industrial installation with honeycomb catalysts. In the course of this procedure, it has to be ensured that the honeycomb bodies do not break down during filling. Considerable emphasis has to be placed on the avoidance of edge flow effects, since otherwise the catalysts are not capable of contributing their full effect. Moreover, honeycomb-shaped catalyst materials exhibit poor thermal condutivity in a radial direction. This is particularly disadvantageous in reactions in which there is considerable evolution of heat, as in oxidation reactions for example. For the aforementioned reasons, there is currently no known industrial application in which a tube bundle reactor or thousands of tubes are operated with honeycomb-shaped catalyst materials. For this reason, reactors are packed with moldings in the form of pellets, which likewise exhibit a low pressure drop.
It is known from EP-B 0 519 435 that SiO
2
can be pressed by means of binders to produce supports, followed by calcining the supports obtained and washing the calcined support particles with acid until cations from the binder are no longer released. In addition, a supported catalyst, a process for the production thereof, and the use thereof for the production of vinyl acetate are also described.
EP-A 0 807 615 describes pressed parts based on pyrogenic silica. These pressed parts can be used as a catalyst or catalyst support for the production of vinyl acetate monomer and for the hydration of ethylene. The pressed parts may be of different shapes, e.g. cylindrical, spherical or annular, with an outside diameter of 0.8 to 20 mm.
SUMMARY OF THE INVENTION
The present invention relates to moldings based on silica, which are characterized in that that the supporting geometry consists of a hollow cylindrical configuration with internal reinforcing stays or spokes leading from the inner wall of the hollow cylinder to the center of the molding, or is characterized by a multiplicity of passageway channels.
The moldings according to the invention can have an outside diameter from 1 to 25 mm and a ratio of height to diameter of 0.2 to 5. Furthermore, they can have a total pore volume of 0.3 to 1.8 ml/g and a BET specific surface of 5 to 400 m
2
/g.
The SiO
2
content of the moldings according to the invention is preferably more than 99.0% by weight. The proportion of other constituents can be less than 0.2% by weight. The moldings according to the invention can therefore be characterized as being free from binders. The fines can amount to less than 5% by weight. The bulk density can range from 100 to 700 g/l.
The present invention further relates to a process for the production of moldings based on silica, which is characterized in that silica is subjected to a kneading and working process, and is then extruded. The extrudate is optionally cut to the desired length by means of a cutting device, is dried at a temperature of 20 to 150° C., and is annealed for a period from 0.5 to 10 hours at a temperature from 400 to 1200° C.
In one particular embodiment of the invention, the silica can be a pyrogenic silica. Silica which can be used according to the invention, which thus includes pyrogenic silica, is described in Ullmanns Enzyklopädie der technischen Chemie, 4th Edition, Volume 21, pages 451 to 476 (1982).
One preferred embodiment of the invention is a process for the production of moldings based on silica, which is characterized in that silica is homogenized with methyl hydroxyethyl cellulose, wax and/or polyethylene glycol with the addition of water and optionally with the addition of an aqueous alkaline ammonia solution, is subjected to a kneading and working process, shaped and/or extruded. The moldings are optionally cut to the desired length by means of a cutting device, are dried at a temperature from 10 to 150° C. and are annealed for a period from 30 minutes to 10 hours at a temperature from 400 to 1200° C.
Kneaders, mixers or mills which enable good homogenization and compaction of the mixed material to be effected, such as blade mixers, fluidized bed mixers, rotary mixers or air jet mixers, for example, can be used for carrying out the process according to the invention. In particular, mixers can be used which make it possible to effect additional compaction of the mixed material, such as plough mixers, kneaders, pan grinders or ball mills. Mixing and kneading can also be effected directly in the extruder. The production of the moldings can be effected in single-screw or twin-screw extruders, in extrusion presses or in tabletting machines. The moldings according to the invention are preferably produced by means of extruders.
In one particular embodiment of the invention, the mixture can have the following composition before it is shaped:
50-90% by weight silica, preferably 65-85% by weight;
0.1-20% by weight methyl hydroxyethyl cellulose, preferably 5-15% by weight;
0.1-15% wax, preferably 5-12% by weight;
0.1-15% polyethylene glycol, preferably 5-10% by we
Kraus Helmfried
Lansink Rotgerink Hermanus
Schinke Peter
Tacke Thomas
Bell Mark L.
Degussa - AG
Hailey Patricia L.
Pillsbury & Winthrop LLP
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